For years, personal computers (PCs) have used the so-called legacy basic input/output system (BIOS) to facilitate booting and to provide an interface between the computer operating system and various input/output (I/O) devices such as displays, keyboards, mice, and disk drives. Over the past several years, however, the Microsoft Corporation has been developing a new software interface, called the extensible firmware interface (EFI), that is expected to replace the legacy BIOS. The EFI provides a new model for the interface between operating systems and platform firmware and comprises data tables that contain platform-related information and boot and runtime service calls that are available to the operating system and its loader. In order to communicate with the EFI, the operating system must be specifically configured for use with the EFI, or other appropriate software must be developed to enable such communication.
Given that it appears that the PC industry will be transitioning to EFI-based systems, it is likely that future PCs will comprise the EFI. At least for the next few years, however, there will be many persons that will still use legacy-based operating systems that cannot communicate with the EFI. Accordingly, needed is an interim solution that supports both legacy BIOS and EFI so as to enable the use of either a legacy-based operating system or an EFI-based operating system.
Although both interface systems could be supported by installing both the legacy BIOS and the EFI in the system memory so that either is available for use, such a solution typically would require a larger system memory device (e.g., flash chip) to store both interface systems. Although such memory devices are available, their use would undesirably increase the cost of the PCs in which they are installed.
The Intel Corporation has proposed an alternative solution. Specifically, proposed is a backward-compatible solution in which the EFI layer is configured to emulate certain aspects of legacy BIOS operation so as to enable interface with legacy-based operating systems. In that solution, a compatibility support module (CSM) comprising a series of drivers chooses a legacy BIOS or EFI booting route depending upon the boot device(s) that is/are selected. Although this solution avoids the memory space problem identified above, such emulation is relatively complex and therefore requires significant time and resources to develop.